Specific Binding of Phosphorylated Non-Histone Chromatin Proteins to Deoxyribonucleic Acid

The binding of phosphorylated non-histone proteins to DNA has been studied via the technique of DNA-cellulose chromatography. At an NaCl concentration of 0.14 m, approximately 1 % of this protein fraction prepared from rat liver binds to rat DNA. Both the percentage of binding observed and the binding constant for the protein-DNA interaction are dependent on ionic strength. The phosphorylated proteins bind less efficiently to foreign DNAs than to host DNA, thereby demonstrating the specificity of the binding reaction. Treatment with various enzymes demonstrates the protein nature of the material involved in conferring the specificity of binding of the non-histone proteins. At physiological ionic strength, binding sites on the DNA are saturated at a value of approximately 1 µg of phosphorylated protein per 100 µg of DNA. The material which selectively binds to the DNA is still a heterogeneous family of phosphorylated proteins as demonstrated via sodium dodecyl sulfate acrylamide gel electrophoresis. The majority of these DNA-binding proteins fall in a molecular weight range of 30,000 to 70,000, and amino acid analyses confirm that these phosphorylated proteins are non-histones. The results are consistent with a proposed role of the phosphorylated non-histone proteins in specific gene control.